Getting the air out is key to Humvee Safety

The tire, developed by Resilient Technologies LLC, Wausau, Wis., along with the DoD and the University of Wisconsin-Madison, is a rubber tread supported by a lattice of plastic hexagons with a central metal bolting hub.

In a war zone, tires are a vehicle’s Achilles’ heel. They can’t be armored, yet bullets, debris, and even rocks can cause punctures and compromise missions. Although the Army uses “run-flat” tires on some vehicles, they provide only limited mobility to get to safety. Humvees go through about 200,000 tires each year, according to an Army spokesman. Similar problems exist on heavy trucks that transport personnel and equipment in the theater.

Going airless seems like a no-brainer. But previous attempts at nonpneumatic tires, or NTPs, haven’t been able to mimic the performance of standard tires. Without the cushioning effect of air, vibrations generate unacceptable noise levels, interfere with onboard electronics, and compromise passenger comfort. Heat doesn’t dissipate efficiently either, leading to dangerously high temperatures in the tires’ rubber. Resilient’s team,

which includes graduate students from UW-Madison, developed the honeycomb structure, a contrast from the airless, spoked “tweel” Michelin, Greenville, S. C., debuted in 2005. The walls of the honeycomb structure spread the load more evenly and let the tires ride more like their pneumatic cousins, Resilient claims. The open structure also permits better heat dissipation.

Aside from the obvious benefit of never going flat, NPTs offer a few other upsides. They may be lighter than standard metal-rimmed pneumatic tires because of their polymer construction and elimination of the need to hold pressure. Vehicles running NPTs would be lighter, too, because they wouldn’t have to carry a spare. Drivers could also skip the air pressure checks needed to ensure the best gas mileage.

On the way to the final configuration being tested on Humvees at Wausau’s National Guard installation, Resilient formulated several rubber and polymer compounds and put them through their physical, mechanical, and environmental paces. The most promising prototypes made it to lawn-tractor size for testing.

So when will NPTs save you from changing a tire in rush-hour traffic? Probably not anytime soon. The $18 million, four-year project is focusing on Humvees, and Army transport vehicles are next on the horizon.

In the civilian arena, construction equipment is a more likely near-term market. The downtime needed to change a tire on a construction site is expensive, and the vehicles don’t go fast enough to encounter significant vibrations or heating. Michelin has focused its tweel efforts on this segment for the time being. Resilient’s General Manager Mike Veihl says that ATVs, heavy mining equipment, and farm machinery could also benefit from air-free tires.

Plans for passenger vehicle tires seem to fall to the bottom of the list. But with gas prices and pressures for fuel economy both rising, a successful Army-tested NPT could make its way to the private sector faster than we think.

The honeycomb structure of Resilient Technologies’ nonpneumatic tire is formed in molds. The company designed the materials and structure in partnership with the UW-Madison Polymer Engineering Center. Photo: Jeff Miller.

Sgt. Robert Hoock with the Army National Guard base in Wausau, Wis., examines the installation of Resilient Technologies’ prototype airless tire. The design is currently being tested on National Guard Humvees and is expected to boost security of vehicles in combat. Photo: Resilient Technologies LLC